We shall continue to work on the enzymatic synthesis of riboflavin with an emphasis on understanding more completely the nature of the enzymatic reactions and the identity of the intermediates involved in the enzymatic transformation of GTP, the ultimate precursor, to riboflavin. We shall concentrate in particular on the enzymatic steps by which 5-amino-2,6-dioxy-4-(5'-phosphoribitylamino)pyrimidine is converted to dimethyl-8-ribityllumazine. In this enzymatic transformation a 4-carbon unit is needed. We have discovered an enzymatic activity in extracts of E. coli that catalyzes this reaction, but we have not yet identified the 4-carbon compound, nor do we known very much about the reaction as regards possible intermediates. We shall also continue our work on the enzymatic synthesis of pteridine pigments in the fruit fly, Drosophila melanogaster, from GTP and dihydroneopterin triphosphate: the latter compound is the common intermediate that appears to be involved in the biosynthesis of all naturally-occurring pterins. The pigments of particular interest for study are sepiapterin, biopterin, pterin, xanthopterin, isoxanthopterin, and the drosopterins.